1. Field of the Invention
The present invention relates to a semiconductor device having a semiconductor element, such as a bare chip, chip size package, or IC module, mounted onto a circuit board by means of a thermosetting resin adhesive.
2. Description of the Related Art
Mounting of a semiconductor element, such as a bare IC chip, on a circuit board is typically carried out by applying a thermosetting insulating adhesive of liquid or film form, such as an epoxy-based resin, between the circuit board and the semiconductor element, and subjecting the semiconductor element to thermocompression with a bonding tool equipped with heating means to effect mounting thereof.
A problem encountered with mounting a semiconductor element provided with tiny bumps to a circuit board having a fine conductor pattern is that voids present in the cured adhesive reduce the adhesive strength and lower connection reliability in humidity resistance tests and heat shock resistance tests. Accordingly, conditions for thermocompression are selected so as to substantially eliminate voids in the adhesive and ensure a reliable degree of adhesive strength.
Conditions for thermocompression include one step conditions, namely, setting the factors of temperature, pressure and time to constant optimal values (for example, constant temperature of 180xc2x0 C., constant pressure of 10 kg/cm2 per IC chip, and constant time of 20 seconds); two step conditions, namely, varying the temperature profile under constant pressure, especially, temperature elevation in two steps (for example, under constant pressure of 10 kg/cm2, temperature 100xc2x0 C./time=10 secondsxe2x86x92temperature=200xc2x0 C./time=10 seconds); etc.
However, a problem encountered with the aforementioned one step conditions, as well as with two step conditions involving varying the temperature profile under constant pressure, is failure to eliminate to a sufficient extent voids present in the adhesive.
The present invention is intended to solve the problems of the prior art described above, and has as an object to provide a process for producing a semiconductor device, comprising mounting of a semiconductor element on a circuit board via a thermosetting resin adhesive, whereby curing of the adhesive may be brought about in such a way that residual voids are eliminated, thereby affording excellent connection reliability.
Focusing upon variation in the pressure profile, a factor having insufficiently taken into consideration, the inventor perfected the present invention on the basis of the discovery that by first conducting compression under relatively high pressure to substantially eliminate voids present in the adhesive, and then proceeding to cure the thermosetting resin under compression at a pressure lower than the pressure in the preceding step, it is possible to significantly reduce residual voids in the cured adhesive, thereby affording more excellent connection reliability.
Specifically, the invention provides a process for producing a semiconductor device, comprising mounting of a semiconductor element on a circuit board via a thermosetting resin-based adhesive by means of a thermocompression process, wherein the thermocompression process is carried out under a first set of conditions (pressure=P1 and temperature=T1) designed to eliminate voids present in the adhesive, and subsequently under a second set of conditions (pressure=P2 and temperature=T2) designed to bring about curing of the thermosetting resin, the pressure P2 of the second set of conditions being set to a lower level than the pressure P1 of the first set of conditions.
These and other objects, features and advantages of the present invention are described in or will become apparent from: the following detailed description of the invention.